The present invention relates to a cathodoluminescent apparatus and a phosphor powder, more precisely relates to a cathodoluminescent apparatus, which illuminates rooms, liquid crystal display devices as a back light, etc., and which can be used as pixel units of large scale video displays, and a phosphor powder for the same.
Conventionally, fluorescent lights are popularly used as room lights. In the fluorescent lights, the ultraviolet light by discharge of mercury vapor irradiates a phosphor screen formed on an inner face of a glass tube so as to convert to visible light.
Conventional fluorescent lights, however, have some disadvantages.
Brightness of the phosphor screen will be increased, if the intensity of the ultraviolet light is increased, but the temperature of the mercury vapor is restricted by physical conditions, so that brightness of the fluorescent light is limited. Therefore, illumination level in rooms is controlled by only the number of fluorescent lights.
To make a plane light source with fluorescent lights, a plurality of fluorescent lights must be arranged in parallel, because fluorescent lights are line light sources, so that the cost must be increased.
Further, the above-mentioned phosphor screen is formed by applying onto a substrate a slurry composed mainly of a mixture of an organic binder solution, such as cellulose nitrate solution, and phosphor powders.
The best fluorescent substance for the slurry application method is such one as is capable of dispersing well in the slurry and producing high light scattering in the phosphor screen in dry state.
In connection with the above, the conventional phosphor powders contain small single crystals in quantity, have low coefficients of light scattering, and have weak strengths of adhesion onto substrates. Owing to these properties, those phosphor screens for which the conventional phosphor powders are used, have encountered a problem with pinholes.
An object of the present invention is to provide a cathodoluminescent apparatus, which is capable of adjusting brightness and which is less expensive and economical, and a phosphor powder, which has tough strength of adhesion onto substrates and high coefficients of light scattering in a dry phosphor screen.
The inventor thought that the object could be achieved by cathodoluminescence, and reached the present invention. The present invention has following structures.
Firstly, the apparatus comprises:
a line electron gun having a line cathode, which is elongated in a first direction, and an intermediate electrode, which is capable of extracted electrons from the line cathode, of linearly focusing electrons extracted, and of reciprocatively scanning electrons focused in a second direction perpendicular to the first direction;
an anode for accelerating electrons emitted from the line electron gun, the anode having an electric conductive section formed on a substrate, wherein voltage is applied thereto for the acceleration;
a phosphor screen being made of phosphor particles on the electric conductive section; and
a container being capable of accommodating the line electron gun and the anode, the container having a light emitting face, through which visible light is capable of passing, the container being evacuated to a vacuum for cathodoluminescence.
With this structure, brightness of luminescence on the phosphor screen can be adjusted by the voltage applying to the intermediate electrode.
Moreover, because the line electron gun focuses and reciproctively scans electrons extracted, a plane light source can be realized with one line electron gun.
On the other hand, the phosphor powder suitably used for the above-described cathodoluminescent apparatus should be composed of primary particles of Y.sub.2 O.sub.2 S polycrystal which are almost spherical with their surfaces formed rough and about 4.5 .mu.m in median diameter so as to pass, for example, through a 400-mesh sieve.